ASK DR. K:

DEAR DOCTOR K: My father has Alzheimer's disease. Is it unsafe for him to drive?

DEAR READER: Alzheimer's disease (AD) is a form of dementia that worsens over time. It often affects short-term memory early on, and then progresses to impair other cognitive functions such as thinking and judgment. As AD advances, most people lose their ability to do normal daily activities. Your question — whether your father should stop driving — is a common concern for families of a loved one with AD.

The automobile has become a part of who we are in the United States. It gives us a sense of independence and the means to go nearly anywhere. Also, in many cities (like Los Angeles, where I was raised), public transportation is not nearly good enough to substitute for an automobile. To lose the freedom to drive and to become dependent on taxis, buses or subways, is for many people a sad thing to contemplate.

But when you drive a car, you control more than a ton of steel moving at high speed. Of course the world around you has to be concerned if you can't control it.

Safe driving requires a complex interaction of eyes, brain and muscles. It also requires the ability to respond quickly to unexpected circumstances. One study found that the driving skills of people with even mild Alzheimer's were significantly poorer than those of other elderly people, including those with some other forms of dementia.

Some people believe that driving privileges should not be taken away until a person clearly becomes an unsafe driver. But it makes no sense to me to say that a person has to prove he or she is an unsafe driver by getting into an accident that was clearly caused by failing faculties — especially when that accident damages more than property.

Your father's general behavior in non-driving situations can give you some clues as to whether safety is likely to be an issue. For example, if your father exhibits poor judgment, inattentiveness to what's going on around him, clumsiness, and slow or inappropriate reactions, then those are clear signs that he should not drive.

If you feel that it is time for your father to stop driving, some experts would suggest that you try simply taking away his keys. If his dementia is substantial, after a period of confusion about where the keys are, he may simply forget about them.

Try to preserve his self-esteem. Some people agree to stop driving for reasons other than concern about their competency. For example, you might tell your father that his car needs repair, or that the license or registration has expired.

Getting objective feedback from an impartial person can help. Some people with AD will accept a written prescription from a doctor that says, "Do not drive." If that doesn't convince him, then his doctor may be able to have his driver's license suspended with a written statement. If nothing else works, you may have to sell the car.

Dr. Anthony Komaroff is a physician and professor at Harvard Medical School. Visit his website at www.AskDoctorK.com. to submit questions and for more information.